gistfile1.txt

use std::collections::VecDeque;
use std::env;
use std::fs;
use std::fs::File;
use std::io::prelude::*;
use std::io::{Error, ErrorKind};
use std::path::Path;

fn help() {
    println!("Usage: decrypt <in> <key> <out>");
}

struct RingData(VecDeque<u8>);

// Implements an endless iterator over a set of data
impl Iterator for RingData {
    type Item = u8;

    fn next(&mut self) -> Option<Self::Item> {
        match self.0.pop_front() {
            Some(current) => {
                self.0.push_back(current);
                Some(current)
            }
            _ => None,
        }
    }
}

fn main() -> Result<(), Box<dyn std::error::Error + 'static>> {
    let args: Vec<String> = env::args().collect();

    if args.len() != 4 {
        help();

        return Ok(());
    }

    let input_data = fs::read(&Path::new(&args[1]))?;

    let header = &input_data[0..=10];
    if !(header.is_ascii() && std::str::from_utf8(&header)? == "AMIROMTYPE1") {
        return Err(Box::new(Error::new(
            ErrorKind::InvalidData,
            "Unsupported ROM file",
        )));
    }
    let mut out_data = Vec::new();

    let key = RingData(VecDeque::from(fs::read(&Path::new(&args[2]))?));

    for it in input_data[11..].iter().zip(key) {
        let (a, b) = it;

        out_data.push(a ^ b);
    }

    let mut out = File::create(&Path::new(&args[3]))?;
    out.write_all(&out_data)?;

    Ok(())
}